Process for preparing spandex filaments



Nov. 19, 1963 J, ROMANQ 3,111,368

PROCESS FOR PREPARING SPANDEX FILAMENTS Filed Jan. 29, 1962 i F 3 f[,. ,v

GAS

INVENTOR JOHN E. ROMANO 40 ATTORNEY United States Patent 3,131,368 PROCESS FUR PREPARING SlANDEX FHAWENT John Romano, H'oelressin, Del, assignor to E. 1.

tin Font de Nemours and Compmy, Wilmington, Bel,

a corporation of Delaware Filed Jan. 29, 1962, Ser. No. 169,217 7 Claims. (Ql. 1S54) This invention relates to a process for preparing spandex filaments. More particularly, the invention relates to a dry spinning process for preparing spandex filaments of uniform denier.

In known dry spinning processes, a heated gas is introduced into a spinning cell to evaporate solvent from the extruded stream of polymer-containing solution. in spinning many polymer compositions no severe problems are encountered in producing uniform filaments if ordinary precautions are taken in introducing and withdrawing the heated gas from the spinning cell. It has been found, however, that in spinning spandex polymer solutions using known processes, considerable variation in the filament denier results. A Zone of turbulence just below the spinneret in the spinning cell produces fluttering in the filaments being formed. This fluttering in the semiplastic filaments, in combination with the tension on the filaments as they are withdrawn from the spinning cell, results in an objectionable denier variation along the threadline.

It is, therefore, an object of this invention to provide a process for dry spinning spandex filaments of uniform denier. It is another object of this invention to increase productivity of dry-spun spandex filaments having superior physical properties. Other objects will appear hereinafter.

The objects of this invention are accomplished by a process which comprises extruding a solution of a spandex polymer into a cylindrical spinning cell from a spinneret having a plurality of orifices arranged in an essentially circular pattern, simultaneously passing a stream of dry, heated gas into the spinning cell at a velocity of less than about 2.5 feet per second in the direction of travel of the filaments, confining the stream of gas to a restricted annular passage encompassing the filaments extending from the point of extrusion of the filaments for a substantial distance along their path of travel, and then re moving the gas at a position along the direction of travel of the filaments remote from the spinneret. Surprisingly, it is found that filament flutter and the accompanying variation in denier along the length of the filaments are substantially reduced. The annular passage must have a cross-sectional area equal to at least 75% of the crosssectional area of the portion of the spinning cell within which the passage is located. The heated gas, which becomes solvent-laden as it passes through the spinning cell, is withdrawn at a position near the bottom of the cell. The filaments are withdrawn from the bottom of the spinning cell in a bundle and passed to appropriate collecting means.

In carrying out the process of this invention, the spandex polymer is dissolved in an inert solvent to provide a spinning solution having a polymer solids content from about to about 30% or more by weight. The spinning solution is heated to a temperature from about to about 100 C. and extruded into the spinning cell. Simultaneously, a uniform stream of gas, heated to a temperature from about 250 to about 400 C., is passed into the spinning cell. The gas which is confined to the annular passage previously described travels at a velocity up to about 2.5, preferably 2 feet per second or less, through the passage, after which it travels to the bottom of the spinning cell where it is withdrawn.

3,lll,3fi3 Patented Nov. 19, 1963 The invention will be further described with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic drawing of suitable apparatus for carrying out dry spinning by the process of this invention;

FIGURE 2 is a cross-sectional view of the apparatus of FIGURE 1 taken along line 22; and

FIGURE 3 is "a side view of a device for providing a restricted annular passage in the spinning cell adjacent to the spinneret.

Referring to FIGS. 1 and 2, a dry, heated gas is introduced into spinning cell 12 through inlet 14 and gas :manifold 4. The heated gas is uniformly distributed by a gas distributor 6 and is directed downwardly into the spinning cell 12 iii an even flow pattern by baifle '8 which is positioned adjacent to spinneret assembly 10. Bafile 8 is positioned to prevent the flow of gas between the ibafile and the spinnerett assembly :but does not protrude below the bottom face of the spinneret. A spinning solution of suitable viscosity is pumped to spinneret assembly 16 and extruded through orifices 16 to provide a plurality of filaments 1. As the filaments 1 enter the spinning cell 12, they first traverse an annular passage where the heated gas enters the circle of filaments. This passage is defined by the walls of spinning cell :12 and the outer surface of a cylindrical body 21 which is centrally positioned in the spinning cell and secured to the face of spinneret assembly 19. Cylindrical body 21 need not extend completely to the face of spinneret assembly 10; however, the clearance should preferably be kept to a During the passage through the cell, the heated gas becomes solvent-laden. Accordingly, a counter-current stream of gas may be introduced through inlet 18 at the bottom of the cell to minimize condensation of the solvent at the bottom of the cell. The two streams of gas meet and are drawn oil evenly around the periphery of the cell wall through an aspirator device 20. The solvent maybe recovered from the gas for reuse. The gas, dried of solvent, may also be reused by reheating it and introducing it again into the spinning cell.

As illustrated in FIG. 1, the filaments 1 are withdrawn from spinning cell 12 through opening 30 as a twisted bundle 26. The bundle may be withdrawn from the cell at a rate from about to 1500 yards per minute. T wisting is accomplished by passing the filament bundle 26 through a jet twister 22 which is supplied with a steady flow of air through inlet 24. As the twist travels upwardly in the spinning cell, a point 27 is reached at which the individual filaments l first contact each other to form a coalesced filament bundle 26. Since the twist is a false twist, the bundle 26 leaves forwarding roll 23 essentially free of twist. The bundle is then passed over a finish roll 32 mounted in trough 33 for application of a lubricant and is then forwarded by roll 34 to a wind-up apparatus consisting of a traversing yarn guide 36 and a drive roll 33, and is then wound up on bobbin 40.

FIG. 3 illustrates an alternate device for cylinder 21 illustrated in FIG. 1. By utilizing the bullet-shaped de vice illustrated in FIG. 3, an annular passage having a constant cross-sectional area adjacent to the spinneret and a cross-sectional area which continuously increases at a rate determined by the contour of the surface at a posi tion remote from the spinneret is provided. Utilizing a Zone of the character just described has been found to be particularly desirable in the process of the present invention.

In practicing the present invention, most advantageous results are obtained by utilizing a flow of heated gas which has a velocity of about 2 feet per second or less, measured at the point of extrusion of the spinning solution. The minimum velocity is not critical. The annular passage should have a cross-sectional area such that the amazes 2.9 ratio of the area of the cross-sectional area of the spinning cell to the cross-sectional area of the annular passage is preferably between about 1002825 and about 100299. The length of the annular passage does not appear to be critical providing the converging bundle of filaments does not contact the surface of the obstructing device. a

The particular dimensions of the annular passage must, of course, be varied, depending on the spinning conditions used, e.g., flow rate of the heated gas in the cell and the geometry of the cell and spinneret. In using a spinning cell having a diameter of about 14 inches at the level of the spinneret and 1a spinneret having an orifice circle of about 6.3 inches in diameter, uniform deniers are obtained by attaching cylinders 3 inches in diameter and from 1 to inches in length to the spinneret face as illustrated in FIG. 1.

The advantages of this invention are realized providing the ratio of the diameter of the cylinders to the diameter of the spinning cell lies between about 1:10 and 5:12. On an area basis, this means that the ratio of the obstructed area to the total cross-sectional area of the cell should lie between about 1:100 and about 1:5.7. When using a cylindrical device, a ratio of length of the cylinder to the diameter of the cylinder between 1:1 and 4:1 has been found to be satisfactory, providing the maximum diameter of the device is less than half that of the cell.

This invention is particularly useful in obtaining high productivity of spandex filaments at moderate rates of solvent removal. Ordinarily, the evaporation load in the practice of this invention is less than about 55 pounds of sol-vent evaporated per hour in a spinning cell. Preferably, the evaporation load is kept below about 42 pounds of solvent per hour.

Multiple-thread spinning from a single cell may be accomplished using the present invention by gathering the filaments issuing from the spinneret into separate groups, e.g., two, four, or eight, and conducting each group of filaments to a separate air jet twister located beneath the cell. This modification is obviously useful when not all of the filaments issuing from a single spinneret are needed to make up the final coalesced multifilament having a specified denier. When multiple-thread spinning is practiced, it is advantageous to use a multi-stream pump, e.g., a four-stream pump, to supply spinning solution to the separate groups of orifices in a spinneret. In this modification, the obstructing device is centrally located, just as when only a single, coalesced multifilament emerges from the cell.

The segmented polyurethanes from which the spandex filaments are obtained are generally prepared from hydroxyl-terminated prepolymers, such as hydroxy-terminated polyethers and polyesters or" low molecular weight. Reaction of the prepolymer with a molar excess of organic diisocyanate, preferably an aromatic diisocyanate, produces an isocyanate-terminated material which may then be chain-extended with a difunctional, active-hydrogen containing compound, such as water, hydrazine, organic diamines, glycols, aminoalcohols, etc. Many segmented polyurethanes of this type are described in several patents and are useful in the practice of this invention. Among these are US. Patents 2,929,800, 2,929,801, 2,929,802, 2,929,804, 2,957,852, 2,962,470, 2,999,839, and 3,009,901. These patents teach that elastic filaments may be made from segmented polyurethanes which contain segments of a high-melting, crystalline polymer alternating in the chain with segments of a low-melting amorphous polymer. The crystalline, high-melting segment may be derived from, for exampl a polyurea, polyurethane, polyamide, or bisureylene polymer. The lowmelting, amorphous segment may be derived from, for example, a polyester, a polyether, or an N-alliylated polyurethane. As taught by the aforementioned patents, many of the segmented polyurethanes when in filament form display elongations at the break in excess of 200%, elastic recovery (or tensile recovery) of above about and stress decay below about 20%.

As indicated hereinbefore, the segmented polyurethanes are preferably prepared by carrying out the polymerization reaction in the solvent to be used for spinning. Conventional procedures may be used for preparing such polymer solutions. Solvents which have been found satisfactory for use in the dry-spinning operation include N,N-dimethylformamide, N,N-dimethylacetamide, tetramethylenesulfone, formic acid, and mixtures of 1,1,2- trichloroethane with formic acid. The spinning solution may contain from 15% to 30% or more of polymer solids, depending on the solvent used and solution properties desired and may be preheated prior to introduction to the spinneret. Vicosities of the order of 400 to 1600 poises are conveniently handled. The intrinsic viscosity of the polymer should be above 0.6, preferably above 1.0.

This invention is further illustrated but is not intended to be limited by the following example in which parts and percentages are by weight.

Example Into a reverse centrifugal mixer maintained at 50 C. are fed a stream of polytetramethylene ether glycol at a rate of 8 pounds per hour and a stream of liquid p,p'- methylenediphenyl diisocyanate at 2 pounds per hour. The polytetra-methylene ether glycol has a molecular weight of about 2000 and is thoroughly pre-dried by treatement with a molecular sieve. The reagents are intimately mixed, remain in the mixer for one minute, and are dicharged continusously into a jacketed pipeline maintained at about 96 C. and extending for 25 feet. The pipeline serves as a reactor in which the polyether glycol is capped with 2 mols of the diisocyanate to yield an isocyanate-termina-ted polyether. The average time spent in the reactor is between 90 and 100 minutes. On emerging from the pipeline reactor, the isocyanateterminated polyether is cooled at once to below 45 C. The cooled isocyanate-terminated polyether is conducted at a rate of 9.2 pounds per hour into a high-shear mixer containing a rotating disc, and a stream of N,N-dimethylformamide is added at 42.8 pounds per hour. The mixture (17.7% solids) is thoroughly agitated for 4 minutes and then passes to a chamber in which a mixture of hydrazine (35% in water) and diethylamine (5% in dimethylformamide), in the ratio of 37.5 parts of hydrazine to 1 part of diethylamine, is added as a single stream at a rate of 0.465 pound per hour with strong agitation. The mixture passes to a reaction chamber held at a temperature of 20 to 40 C., the contents having a residence time of about 2-3 minutes. The emerging polymer solution contains approximately 17.7% solids and has a viscosity of 700 poises at 30 C. The polymer has an inhere-ht viscosity of 1.5. To the polymer solution are added a slurry of titanium dioxide in dimethylformamide and a solution of poly-(N,N diethyl-beta-aminoethyl methacrylate) in di-methylforma-mide such that the final mixture contains 5% of each additive based on the ela tomeric solids.

The foregoing mixture is heated to a temperature of 70 C. and extruded through a tspinneret containing 43 holes into a spinning column 20 feet in length. Kemp gas, essentially a mixture of about 87% nitrogen and 13% carbon dioxide, heated to 340 C. is introduced at the top of the spinning column and is drawn oil at a point about 4 feet above the exit point of the filament bundle.

At the level of the spinneret, the spinning'cell has an inner diameter of 14 inches. The spinneret assembly is 7.25 inches in diameter and contains a single circle of orifices, each of which is 0.007 inch in diameter. The circle of orifices has a diameter of 6.3 inches. In passing the face of the spinneret, the Kemp gas used at a rate of pounds per hour has a velocity of about 2 feet per second. Directly below the center of the spinneret and within the circle of or-ifices is attached a cylinder of sheet metal 4.5 inches in diameter and 5 inches long, thereby confining the heated Kemp gas to an annular passage between the walls of the spinning cell and the cylinder. The top of the cylinder is less than 1 inch from the face of the spinneret.

Below the column, the filament bundle passes through a jet twister which backs twist up the bundle into the column to a point about 9 feet above the exit. The wellcoalesced multifilament of about 280 denier leaving the jet is passed over a roll turning at a linear speed of 535 yards per minute, is treated with an oil-based finish, is passed over another roll turning at 535 yards per minute, and is wound up at 532 yards per minute.

The coeficient of denier variation along the length of the product is found to have an average value of 3.81%. Under identical spinning conditions, but without the cylinder attached to the face of the spinneret, the coefiicient of denier variation has an average value of about 5.79%.

The coeificient of denier variation (percent CDV) is calculated from the following formula:

where 0' is the one standard deviation calculated on individual denier determinations made along short, cut lengths, e.'g., 9 centimeters, of fiber over a relatively long, continuous length of fiber, e.-g., 9 meters, and X is the average denier along the long continuous length of fiber, e.g., 9 meters.

The process of the present invention has the advantage that it permits a dramatic decrease in denier variation along the length of dry-spun spandex filaments. Because of the fact that there is a marked reduction in filament flutter in the vicinity of the spinneret, the process of this invention permits closer spacing of the orifices in a spinneret and permits higher flow rates of aspiration gas in dry spinning of spandex. As a result, increases in productivity have been made possible which heretofore were not attainable without the accompanying undesirable denier variation in the filaments.

The filaments produced according to this invention find particular utility in foundation garments, girdles, corsets, surgical hosiery, woven or knitted swimwear, socks, and sock tops.

As many widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for preparing spandex filaments of uniform denier which comprises:

(a) extruding a solvent-containing solution of a spandex polymer into a spinning cell from a spinneret having a plurality of orifices arranged in an essen tially circular pattern to form said filaments,

(1)) simultaneously introducing a stream of heated gas into said spinning cell in advance of said spinneret in the direction of travel of said filaments at a velocity of less than about 2.5 feet per second, said velocity being measured in said spinning cell at the point of extrusion of said filaments,

(c) confining said stream of heated gas to a restricted Percent CDV= annular passage encompassing said filaments, said passage being adjacent the point of extrusion of said filaments and extending for a substantial distance along their path of travel and having a transverse cross-sectional area at least three-fourths of the crosssectional area of said spinning cell, and

(d) continuously withdrawing said filaments and removing said gas from said spinning cell at a position along the direction of travel of said filaments remote from said spinneret.

2. The process of claim 1 wherein a major portion of said annular passage adjacent said spinneret "has a constant cross'sectional area and a minor portion of said passage remote from said spinneret has a cross-sectional area which continuously increases until the cross-sectional area of said passage equals the cross-sectional area of said spinning cell.

3. The process of claim 2 wherein said solution of spandex polymer contains from about 15% to about 30% polymer solids.

4. A process for preparing spandex filaments of uniform denier which comprises:

(a) extruding a solvent-containing solution of a spandex polymer at a temperature from about 20 to about C. into a cylindrical spinning cell from a spinneret having a plurality of orifices arranged in an essentially circular pattern to form said filaments,

(b) simultaneously passing a stream of dry gas heated to a temperature from about 250 to about 400 C. into said spinning cell in advance of said spinneret at a velocity of less than about 2.5 feet per second in the direction of travel of said filaments, said velocity being measured in said spinning cell at the point of extrusion of said filaments,

(c) confining said stream of gas in said spinning cell to a restricted annular passage defined by the walls of said spinning cell and an obstruction intermediate the center of said spinning cell and said filaments, said passage being adjacent the point of extrusion of said filaments and extending for a substantial distance along their path of travel and having a transverse cross-sectional area at least three-fourths of the crosssectional area of said spinning cell; and

(d) continuously withdrawing said filaments from the bottom of said spinning cell and removing said gas at a position near the bottom of said spinning cell.

5. The process of claim 4 wherein a major portion of said annular passage adjacent said spinneret has a constant cross-sectional area and a minor portion of said passage remote from said spinneret has a cross-sectional area which continuously increases until the cross-sectional area of said passage equals the cross-sectional area of said spinning cell.

6. The process of claim 5 wherein said solution of spandex polymer contains from about 15% to about 30% polymer solids.

7. The process of claim 6 wherein said filaments are withdrawn from said spinning cell at a rate from about 100 to 1500 yards per minute.

References Cited in the file of this patent UNITED STATES PATENTS 1,942,540 Dreyfus et al Jan. 9, 1934 2,615,198 Flannagan Oct. 28, 1952 2,929,801 Koller Mar. 22, 1960 

1. A PROCESS FOR PREPARING SPANDEX FILAMENTS OF UNIFORM DENIER WHICH COMPRISES: (A) EXTRUDING A SOLVENT-CONTAINING SOLUTION OF A SPANDEX POLYMER INTO A SPINNING CELL FROM A SPINNERET HAVING A PLURALITY OF ORIFICES ARRANGED IN AN ESSENTIALLY CIRCULAR PATTERN TO FORM SAID FILAMENTS, (B) SIMULTANEOUSLY INTRODUCING A TREAM OF HEATED GAS INTO SAID SPINNING CELL IN ADVANCE OF SAID SPINNERET IN THE DIRECTION OF TRAVEL OF SAID FILAMENTS AT A VELOCITY OF LESS THAN ABOUT 2.5 FEET PER SECOND, SAID VELOCITY BEING MEASURED IN SAID SPINNING CELL AT THE POINT OF EXTRUSION OF SAID FILAMENTS, 